Determination of the absolute concentrations of monoamine oxidase A and B in human tissues.

The concentrations of monoamine oxidase-A and -B were determined in homogenates of human cerebral cortex, caudatus and placenta and in human platelet-rich plasma and platelet membranes by determining the specific binding of tritium-labelled pargyline. The concentrations of the two enzyme forms were similar in both human brain regions examined. Determinations of the minimum quantities of clorgyline, (-)-deprenyl, J-508 or pargyline necessary to give complete inhibition of enzyme activity was found to give overestimates of the amounts of monoamine oxidase-A and -B present due to nonspecific binding of these inhibitors.